The continuing development of optical components such as waveguide gratings (PHASAR “phase array” or AWG “array waveguide grating”), in which a plurality of in-/outputs are formed via optical waveguides and optical signals are transmitted with the aid of carrier wavelengths that are selected ever more closely adjacent, is leading to an intensification of the coupling conditions with regard to the interface of the optical waveguides with the optical component. Such optical components must remain capable of functioning as well as possible under very different conditions. Amongst other things, the functionalities of the optical components must remain independent of the major temperature variations to which they can be exposed. Optical components are formed from a carrier, which can be sufficiently deformed e.g. by temperature variations of this kind or also due to the weight distribution imposed on it, that the optical in-/outputs can be affected by it. In the worst case, such deformations can lead to such a poor alignment of optical in-/outputs, which alignment can lead to a noticeable impairment of the transmission of optical signals.
To compensate for such alignment errors in the optical in-/outputs, specific coupling devices are used. These consist mainly of a carrier of the respective optical in-/outputs and at least one support to the optical component. The carrier is connected to the support such that a change in the alignment of the end of the optical waveguide carried is permitted. An optical coupling device of this kind is described in WO 98/13718. The connection presented there (see enclosed FIG. 1) between the carrier 7 and support 4 is formed by an expansion element 10. Expansion elements of this kind can be made e.g. of a piezoelectric material. In this case, the controlled application of a voltage to the expansion element leads to the alignment of the end of the optical waveguide. It is even possible with the aid of such an optical coupling device to fix the central wavelength of a waveguide grating by the position of the waveguide to be connected that conducts the light into the injection waveguide of the waveguide grating. In this way the central wavelength of the waveguide grating can be adjusted accurately due to the geometrical positioning of the end surface 6 of waveguide 2 in relation to the end surface 5 of the injection waveguide of this waveguide grating.
It is even possible to form an adjustable or flexible waveguide grating. With the aid of such a coupling device, a certain output wavelength of the waveguide grating can be selected, e.g. central wavelength, for adaptation to the operating requirements, to compensate for the aging of transmitter lasers, for example.
The optical coupling device disclosed in WO 98/13718 consists of a holder 3 with a support 4 to the optical component and a carrier 7 for the optical waveguide 2, the carrier 7 being held by the support 4 via the variable-length element 10. Vibrations or bending of the variable-length element 10 and thus temporary or permanent misalignment of the end of the optical waveguide can occur in this case, although some control of the alignment is provided by the variable-length element. A diagrammatic assessment of the curvature of the optical component is shown in FIG. 2. The optical components used, manufactured from a silicon substrate and glass layer, are not actually perfectly flat owing to the different thermal expansion properties of these materials. The optical component accordingly has a curvature of a radius of approx. 15 m. For a holder 3 with a variable-length element 10 that is 15 mm long and a 2 mm thick carrier 7, d=17. The deviation h1 of the end surface 6 of the optical waveguide 2 held by the carrier 7 from the surface 5 of the optical component can amount to 7 μm. This leads to an unacceptable loss of up to 3 dB.
An optical coupling device (see enclosed FIG. 3) is described in WO 01/07949 and consists of two supports 4a, 4b, between which a variable-length element 10 is incorporated. The mounting of the optical waveguide 2 is held by a carrier 7′ on one side on the variable-length element 10 and on the other side by the one support 4b. This support 4b is formed sprung here. Thus movement of the variable-length element 10′ and the carrier 7 of the optical waveguide 2 is permitted in a longitudinal direction of the variable-length element 10′ in which the variable-length element expands or contracts. On the other hand, movement of the variable-length element 10′ perpendicular to the longitudinal direction of the variable-length element is prevented, the sprung support 4b being held close to the fixing of the optical coupling device to the position of the optical component to which the end of the optical waveguide is to be aligned. This support 4b should be formed such that the optical waveguide is held via this sprung support as close as possible to the fixing. The variable-length element 10′, which is unavoidably fastened further away on the optical component, presses the carrier 7′ of the optical waveguide 2 against the support 4b and thus facilitates a movement of the optical waveguide 7′ relative to the optical component. The sprung support 4b is designed such that a residual movement perpendicular to the plane is suppressed as fully as possible. This should lead to the movement of the optical waveguide 2 relative to the optical component being executed very exactly parallel to the surface 5 of the optical component and virtually no misalignment occurring perpendicularly to this.
The losses with such an optical coupling device can be assessed with reference to FIG. 4. With a variable-length element 10′ of a length of 15 mm and a carrier 7′ for the optical waveguide 2 of a diameter of 4 mm, d comes to 17 mm in total. At a distance of the carrier 7′ from the sprung support 4b of 1 mm, the distance d2 between the optical waveguide 2 and this sprung support 4b is roughly 3 mm. If the optical component has a radius of curvature of 15 m, the deviation h resulting from this will be 0.9 Em. In comparison with the previous example in FIG. 2, the loss will only be 0.2 dB.
However, the dimensions of an optical holder 3′ of this kind with 2 supports 4a and 4b are very large. The total length is approximately 25 to 30 mm and can thus be greater than some optical components, e.g. waveguide gratings with a smaller number of channels. Such holders 3′ can therefore only be used for very large optical components. In addition, the structure of such a holder is aggravated by the size, particularly in the event that the material for the supports is selected according to the expansion property of the optical component.